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Thread: Power Supply Recommendation

  1. #1

    Default Power Supply Recommendation

    Just took delivery a Yaesu FTM-400XDR and want to first use it in the shack. Looking for recommendations for a power supply. The radio at max draw pulls around 13 amps. I may want a power supply that would run a couple of mobile radios down the road.

  2. #2

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    Astron RS 35M

    It is said that a 100w HF radio will draw about 22 amps and a 50w FM radio will draw about 10 - 12 amps.

    Since you can only transmit on one at a time,you can run both on this one power supply.

    Linear power supplies are at best about 75% efficient, so you need a safety factor, if you are going to run a 100w HF radio you need a power supply that produces at least 30% more power..

    Avoid switch mode power supplies, they are cheap, but they are noisy and they aren't as reliable.

    The purpose of the meters is to show you what the power supply is doing.. If you have a problem you can see it if you have meters..
    https://www.astroncorp.com/linear-desktop-w-meters

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    gnuuser's Avatar
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    I constructed my own by converting a 600 watt pc power supply ( there are many site that you can view on instructions to do this)
    with the silent cooling fans its reasonably quiet and provides a butt-load of power (about 44 amps)
    too much blood in my caffeine system.

  5. #5

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    Quote Originally Posted by gnuuser View Post
    I constructed my own by converting a 600 watt pc power supply ( there are many site that you can view on instructions to do this)
    with the silent cooling fans its reasonably quiet and provides a butt-load of power (about 44 amps)
    Most (not all) PC supplies are a bit noisy and the 12v they output drops a little when keyed down on a ham radio, making them a bit low on the voltage side of things for most finals. I've killed several running car audio amplifiers on them. If you can crank it up to at least 13v and filter the kHz garbage out, absolutely.

    I bought a computer from cyberpower pc in 2015 and, well, they must have stiffed me on the power supply because this 800w 80+gold that cranks out 60A @12v shats all over my radio.

  6. #6

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    Quote Originally Posted by gnuuser View Post
    I constructed my own by converting a 600 watt pc power supply ( there are many site that you can view on instructions to do this)
    with the silent cooling fans its reasonably quiet and provides a butt-load of power (about 44 amps)
    PC Power Supplies do not offer enough rectification. They are a poor choice for a Linear Power Supply..

    I have a RS35M here that was owned by a locally famous repeater builder, it was dropped, abused, left to rust in his basement.
    The meters fell out, the switch wore out, and yet when I plugged it in it still worked.

    Cost me double what it was worth to restore it, but now it sits on a shelf as a reminder to never take anyone at their word when they say - it works good, nothing wrong with it.

    Most good linear power supplies, when used as designed, will outlive two or three operators!

  7. #7

  8. #8

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    Personally, I use a 220Ah Caterpillar battery with a Beleeb CL-C40 battery charger (not a smart charger). The charger makes absolutely no noise on any of my radios and the battery can take anything I throw at it. And when the power goes out, absolutely nothing at my desk changes.

    Linear regulators are definitely the cleanest, but hardly efficient. Switch-mode power supplies can be amazing if you find one that was built right. Buck-boost circuits can be extremely efficient and, if properly designed and filtered, will put linear supplies to shame. Good linear supplies can be just as hard to find too. Many of them have transformers that put out way too high voltage (because a higher voltage means smaller wire inside it for a given wattage) and the transistor has to work its butt off. If you pull 20A at 12v when the transformer (after rectification and under load) is giving the transistor 24v, the transistor is putting out (24-12)*20 = 240w worth of heat at the same current. The trick is to find a good linear supply with a transformer that puts out ~14Vrms and a ton of current so when it is under load, the transistor only has to eat a volt or two at the same current. That means added weight and added expense on the copper side of things.

    Switch-mode supplies use a higher frequency (thus smaller transformers with more efficient core materials) and higher voltage (thus thinner wire) and PWM circuits that turn solid-state switches on and off to charge a capacitor under load to a set voltage (because ON - there is no voltage drop, and OFF - there is no current, thus no power lost in either state ~ unlike a linear supply with a transistor halfway on). SMPS's use op-amps and a variable reference source to change the duty cycle of the PWM that charges the capacitor to keep it at a set voltage as the load changes.

    Long story short, switch-mode supplies are ages beyond linear supplies, but due to "build it cheap, sell it cheap, buy it cheap (and expect gold)", they caught a bad rep. Don't buy from China and don't use a Walmart "smart" battery charger!
    Last edited by brandon lind; Fri 3rd Jul 2020 at 00:22.

  9. #9

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    Commercial tower sites uses batteries, as does Ma Bell - with their copper line service, and most if not all cell towers should have a battery back up - good for at least 36 hours - continuous duty.

    When I was first licensed I operated my station with the help of 4 wet cell automotive batteries - 750 - 1000 cca each.

    The problem was that batteries eventually wear out and it costs too much to replace them.

    Even commercial tower sites, they replace their standby batteries once every 4 - 5 years, which gets very expensive when there is at least 10 batteries per a site. The only good thing from using batteries is that you have excellent lightning protection - since most lightning come in through the power lines not the antenna. The batteries filters the power going to the radios and protects them from lightning.

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